Deck 28: Temperature and Body Fluid Regulation

Question 1

Every animal's physiological functions are linked to its body temperature because metabolism and enzyme functioning are temperature dependent. Ectotherms derive most of their body heat from the environment, whereas endotherms obtain heat from cellular processes. The evolutionary significance of the rete mirabile is that it acts as a heat generator and enables those fishes that posses it to swim faster and capture more prey.
Based on what you have learned in this section, why are the terms "cold blooded" and "warm blooded" outmoded and inaccurate with respect to describing temperature regulation in animals?

Answer 1

The current distinction should be between the ability to generate metabolic heat in an animal in order to modulate body temperature or the lack of that ability. "Warm-blooded and "cold-blooded" are adjectives that describe the temperature of the blood and not how an animal modulates that temperature. Thus, ectotherms and endotherms are more current and descriptive from a physiological point of view.

Question 2

Why do very small birds and mammals go into a state of torpor at night?

Answer 2

Homeotherms are animals which can maintain a constant body temperature by means of metabolic activity. Their body temperature is mostly more than its environment. Most birds and mammals are homeotherms. But there are some mammals and birds that are so small, that they need constant source of energy in the form of food to generate enough heat to keep them warm.
Due to their low body mass, the loss of heat through their relatively larger body surface area is higher than the heat generated. Thus they spend much of their day sourcing food as a constant source of energy for metabolism.
These small mammals and birds can rapidly run out of energy, if they are not feeding. Thus as a result the only option to conserve energy is by reducing the metabolic rate considerably and by decreasing the body temperatures almost equal to the surroundings.
This sleep-like state of dormancy, which most small mammals and birds enter at night, reducing their metabolic rate and lowering their body temperature is known as daily torpor.
Torpor helps small birds and mammals, reduce the need for food and maintaining a lower body temperature by reducing the metabolism.

Question 3

Most birds and mammals are called

A) ectotherms.
B) endotherms.
C) homeotherms.
D) heterotherms.
E) both b and c.

Answer 3

E
There are various ways by which animals adjust themselves to fluctuations in environmental temperatures. Animals are classified in two ways- depending on their source of body heat they are classified as ectotherms or endotherms; and depending on whether they have a constant or variable body temperature they are classified as homeotherms and heterotherms.
Ectotherms are those animals that derive body heat mainly from the environment. These animals are also known as poikilotherms and have low rates of metabolism apart from being poorly insulated.
Examples are fish and insects.
Thus option (a)
Endotherms are animals that produce body heat from cellular processes. They have a constant source of internal heat and thus maintain a constant internal core temperature. Examples are birds and mammals. Though this is true, birds and mammals fall in another category of classification as well.
Thus option (b)
Homeotherms are animals that maintain a relatively constant body temperature. Examples are birds and mammals. Though this is true, birds and mammals are endotherms as well.
Thus option (c)
Heterotherms are animals that have variable body temperatures and change the internal temperature according to changes in the external environment. Examples are amphibians and some reptiles.
Hence option (d)
Most birds and mammals are both endotherms and homeotherms as they maintain a constant body temperature by obtaining heat from cellular processes.

Question 4

Osmotic balance must be maintained in an animal so that tissues can carry out metabolic functions in a homeostatic state. Physiological mechanisms help most vertebrates keep blood osmolarity and various ion concentrations relatively constant (homeostasis). Marine invertebrates are osmoconformers in that their body fluids are isosmotic to their environment. Most vertebrates are osmoregulators in that their body fluids are either hyperosmotic or hypoosmotic compared to their environment.
During osmosis, does water move toward regions of higher or lower osmolarity (see figure 2.10)?
FIGURE 2.10 Osmosis. ( a ) A selectively permeable membrane separates the beaker into two compartments. Initially, compartment 1 contains sugar and water molecules, and compartment 2 contains only water molecules. Due to molecular motion, water moves down the concentration gradient (from compartment 2 to compartment 1) by osmosis. The sugar molecules remain in compartment 1 because they are too large to pass across the membrane. ( b ) At osmotic equilibrium, the number of sugar molecules in compartment 1 does not increase, but the number of water molecules does.

Question 5

How does the countercurrent mechanism help regulate heat loss?

Question 6

Contractile vacuoles are found in protozoa; protonephridia are found in some flatworms; metanephridia are found in earthworms; antennal (green) glands are found in crayfish; Malpighian tubules are found in insects; coxal glands are found in arachnids; and nephridia in molluscs.
How are the functions of the Malpighian tubules different from the functions of other invertebrate excretory structures?
FIGURE 28.14 Coxal Glands in Arachnids. ( a ) The gut and excretory systems of a spider. The stercoral pocket is a diverticulum off the hindgut that stores waste prior to waste elimination. ( b ) Coxal gland muscles attach to the thin saccular filtration membrane. These muscles promote filtration and fluid flow (black arrows) by contracting and relaxing along the tubular duct. Water and solutes are reabsorbed along the tubular duct.

Question 7

In endotherms, what controls the balance between the amount of heat lost and the amount gained?

Question 8

The hormonal triggering of heat production is called
a. shivering thermogenesis.
b. gular flutter.
c. thermogenesis.
d. nonshivering thermogenesis.
e. hibernation.

Question 9

In the vertebrate kidney, the three key physiological processes used in osmoregulation and excretion are filtration, reabsorption, and secretion. Freshwater fishes must keep water out and retain electrolytes. Marine fishes must keep water in and excrete electrolytes. Water and certain solutes move out of the blood and into the tubular systems of the kidney by way of filtration (passive) and secretion (transported). The important solutes, ions, and water are then returned to the blood through reabsorption. The mammalian kidney is divided into a cortex and a medulla. Within each kidney are about a million nephron units-the functional units of the kidney. The parts of the nephron include the glomerulus and glomerular capsule, proximal tubule, loop of the nephron, distal tubule, and collecting duct.
Mammals and birds have nephrons with a loop of the nephron but reptiles do not. How would you explain this from an evolutionary point of view?

Question 10

If marooned on a desert isle, do not drink seawater; it is better to be thirsty. Why is this true?

Question 11

Which of the following is a function of the kidneys?

A) The kidneys remove harmful substances from the body.
B) The kidneys recapture water for use by the body.
C) The kidneys regulate the concentration of ions in the blood.
D) All of these (a-c) are functions of the kidney.

Question 12

Humans excrete their excess nitrogenous waste as

A) uric acid crystals.
B) molecules containing proteins.
C) ammonia.
D) urea.

Question 13

An osmoregulator would maintain its internal fluids at a concentration that is __________ relative to its specific surroundings (environment).

A) isosmotic
B) hyperosmotic
C) hypoosmotic
D) All of these (a-c).

Question 14

Reptiles are said to be behavioral homeotherms. Explain what this means.

Question 15

Which of the following represents heat loss from an animal's body due to the movement of air over the animal's body?

A) Conduction
B) Convection
C) Evaporation
D) Radiation
E) None of the above (a-d)